The present invention relates to a composite high frequency apparatus, and more specifically, to a composite high frequency apparatus including a high frequency device, for example, a high frequency switch, and a filter and to a method for forming a composite high frequency apparatus by simultaneously forming an interconnected apparatus including at least one high frequency device and at least one filter.
A high frequency switch shown in FIG. 10 is used for switching connections between a transmission circuit TX and an antenna ANT and between a receiving circuit RX and an antenna ANT via signal lines in a portable digital telephone set, for example.
An example of a high frequency device, such as a high frequency switch, has a configuration shown in the circuit diagram of FIG. 11. The high frequency switch 1 is connected to an antenna ANT, a transmission circuit TX and a receiving circuit RX by signal lines V1. A high frequency component, such as a diode D1, has an anode that is connected via a capacitor C1 to the transmission circuit TX. The anode of the diode D1 is also connected to a ground via a series circuit including a strip line L1 forming part of a first transmission line and a capacitor C4. The length of the strip line L1 is substantially equal to or less than .lambda./4, where the wavelength of a signal sent from the transmission circuit TX is .lambda.. A control terminal Vc1 is connected to an intermediate point between the strip line L1 and the capacitor C4. A control circuit (not shown) for switching the high frequency switch 1 is connected to the control terminal Vc1. A series circuit including a strip line L3 forming part of the first transmission line and a capacitor C6 is connected to both ends of the diode D1 (between the anode and the cathode). The cathode of the diode D1 is connected to the antenna ANT via a capacitor C2.
The receiving circuit RX is connected to the capacitor C2, which is connected to the antenna ANT, via a series circuit including a strip line L2 forming part of the first transmission line and a capacitor C3. As in the case of the strip line L1, the length of the strip line L2 is substantially equal to or less than .lambda./4. Another high frequency component, for example, a diode D2, has an anode connected to an intermediate point between the strip line L2 and the capacitor C3. The cathode of the diode D2 is connected to a ground via a capacitor C5. Further, a control terminal Vc2 is connected to an intermediate point between the diode D2 and the capacitor C5. A control circuit (not shown) for switching the high frequency switch 1 is connected to the control terminal Vc2 to thereby complete the circuit of the high frequency switch 1.
When a signal is transmitted through the high frequency switch 1, a positive bias voltage is applied to the control terminal Vc1 while a negative bias voltage is applied to the control terminal Vc2. As these voltages work as bias voltages in the forward direction to bias the diodes D1 and D2, the diodes D1 and D2 will be turned ON. At this time, direct currents will be cut by the capacitors C1 to C6 and the voltages applied to the control terminals Vc1 and Vc2 will be applied only on a circuit including the diodes D1 and D2. Thus, the strip line L2 will be grounded by the diode D2 and will resonate at a transmission frequency and impedance will be made almost infinite. Consequently, a signal sent from the transmission circuit TX will be transmitted to the antenna ANT through the capacitor C1, the diode D1 and the capacitor C2 without being transmitted to the side of the receiving circuit RX in most cases. Further, because the strip line L1 is grounded via the capacitor C4, the strip line L1 will resonate at a transmission frequency and impedance will be made almost infinite. As a result, leakage of a transmitted signal to the ground side will be prevented.
On the other hand, at the time of receiving a signal, a negative bias voltage will be applied to the control terminal Vc1 while a positive bias voltage will be applied to the control terminal Vc2. As these voltages work as bias voltages in reverse directions relative to the diodes D1 and D2, the diodes D1 and D2 will be turned OFF, and thereby a signal received from the antenna ANT will be transmitted to the receiving circuit RX through the capacitor C2, the strip line L2 and the capacitor C3 without being transmitted to the transmission circuit TX in most cases.
In this way, the high frequency switch 1 allows switching of transmitted and received signals by controlling bias voltages to be applied to the control terminals Vc1 and Vc2.
Further, the series circuit including the strip line L3 and the capacitor C6 are used for increasing impedance on a connection point with the strip line L3 when the diode D1 is OFF and for reducing insertion loss and reflection loss by forming a parallel resonance circuit to be resonated by synthetic capacitance between the capacitor C6 and the diode D1 which is OFF and the inductance component of the strip line L3, and by resonating at its resonance frequency which is substantially the same as a frequency of a received signal.
Besides the circuit construction of a high frequency switch described above, there are various types of high frequency switches available. For example, a high frequency switch as described in Japanese Laid-Open Patent No. 6-197042 and Japanese Laid-Open Patent No. 6-197043 and a high frequency switch having a circuit configuration such as the one shown in Japanese Laid-Open Patent No. 7-74762 can also be used.
Further, other high frequency components such as transistors, FETs, and any other suitable device can be used instead of the high frequency components, such as the diodes D1 and D2 described above. In addition, instead of the strip lines L1, L2 and L3, other transmission lines such as coplanar lines and any other suitable components can be used.
Conventionally, however, problems occur when high frequency devices, such as high frequency switches, are used to form a high frequency apparatus by connecting filters to the high frequency devices. The high frequency devices and filters are designed and manufactured differently and independently and are then connected to each other. As a result, the combined high frequency device and filter occupy relatively large areas on a printed circuit board and make the circuit arrangement thereof more complicated. In addition, impedance matching between the high frequency device and the filter must be done to connect the high frequency device and the filter. Therefore, an impedance matching circuit must be designed specifically for the particular high frequency device and filter to be connected to each other. Once the impedance matching filter is designed, the impedance matching filter must be manufactured and connected to the high frequency device and the filter. Consequently, the cost, time and difficulty of manufacturing an apparatus having an interconnected high frequency device and filter with necessary impedance matching circuit is substantially increased.